Hot-isostatic presses (HIPs) adapted for rapid cooling of the load after pressing are known. Such a HIP comprises a pressure vessel in which is arranged a hot zone surrounded by heaters and a thermal barrier. The walls of the pressure vessel are cooled to prevent harmful heating of the pressure vessel. This is utilized when cooling the load in such a way that a circulation loop is produced between the hot zone and the space between the outside of the thermal barrier and the inside of the cooled vessel wall by providing the thermal barrier with at least one opening at the bottom and top, respectively, of the hot zone. Additional cooling of the gas may be achieved by allowing the gas to pass through a heat exchanger, heat-absorbing bodies or the like. To prevent gas circulation during the press cycle, it is known to provide the openings at the bottom or the top with an externally controllable valve (see, e.g. SE 7605887-4). A type of HIP, a so-called modular HIP, for example according to EP 145 417, in which a furnace chamber is placed in a movable chamber, may be provided with an externally controllable valve in both the upper and lower openings in the thermal barrier sealing the furnace chamber during heating and transport outside the pressure vessel. When the chamber is installed in the furnace vessel, the upper valve is opened to allow pressurization to take place.
During the pressing it is important to achieve a uniform temperature in the hot zone to obtain the desired properties of the material. Openings in the thermal barrier and open valves mean that colder gas falls into the hot zone during the press cycle and cools parts of the load. This has resulted in a limitation of the size of the openings provided in the thermal barrier.
During the cooling phase, however, the aim is to achieve a considerable gas circulation which provides rapid cooling. Therefore, it has entailed difficulties to combine requirements for high temperature uniformity during the pressing and a high cooling rate after the pressing.